1. Field of the Invention
The invention relates to a process for the manufacture of a thermoplastic composition. In particular, the invention relates to a process for the manufacture of a thermoplastic composition comprising polyphenylene ether resin.
2. Brief Description of the Related Art
Poly(phenylene ether) resins (referred to hereafter as "PPE") are commercially attractive materials because of their unique combination of physical, chemical, and electrical properties. Commercially, most PPE are sold as blends with predominantly high impact polystyrene resins. PPE are miscible with polystyrene resins in all proportions and because of the very high glass transition temperatures of PPE, the blends of PPE with polystyrene resins possess higher heat resistance than that of the polystyrene resins alone. Moreover, the combination of PPE with high impact polystyrene resins results in additional overall properties such as high flow and ductility. Examples of such blends can be found in U.S. Pat. Nos. 3,383,435; 4,097,550; 4,113,800; 4,101,503; 4,101,504; 4,101,505; 4,128,602; 4,139,574; and 4,154,712 among others. The properties of these blends can be further enhanced by the addition of various additives such as impact modifiers, flame retardants, light stabilizers, processing stabilizers, heat stabilizers, antioxidants and fillers.
Commercial PPE are produced as a relatively fine powder form typically having at least 10% by weight, often at least 20% by weight fine particles of less than about 75 microns in size. Particles less than about 75 microns in size are believed to lead to dust explosion hazards. Consequently these powders require special handling procedures to control dust and potential spark ignition hazards associated with such powders. Such handling procedures include grounding of equipment and use of inert gas blankets to exclude oxygen. It would be commercially advantageous to be able to ship PPE to various locations around the world for compounding into resin compositions to serve local market needs. However, the handling procedures as described above require significant investment for equipment modifications and consequently limit the commercial feasibility for such compounding flexibility. Conversion of PPE powder using standard compounding extruders followed by pelletization of the extrudate to obtain pellets having dimensions of about 3 mm by 3 mm has been attempted as a solution to the problems associated by PPE powder. Unfortunately, the physical properties of many resin compositions made using the pellets are inferior as compared to control compositions made with PPE powder and the pellets must be ground to a smaller size in order to obtain physical properties that closely approximate those of control compositions. Consequently, the utility of the PPE pellet approach has been limited.
It is therefore apparent there continues to be a need for improved processes to manufacture resin compositions containing PPE.